The present invention relates to an RF amplifier control circuit of a disk driver and, in particular, to a DVD system.
FIG. 1 shows a conventional disk driver for use as parts of an audio-video apparatus or a computer peripheral equipment.
Data is stored as a pit array on a spiral track in a disk (CD, CD-ROM, CD-R, CD-RW, DVD-ROM, DVD-RAM, DVD-Audio, DVD-Video, etc.). The reproduction, that is, the reading, of the data is effected by irradiating the pit array on a disk 11 with a laser beam and detecting a reflected laser beam from the pit array.
Upon data reproduction, the rotation speed of the disk 11 is controlled by a disk motor 13 in accordance with a data reproduction scheme. That is, upon CLV (Constant Linear Velocity) reproduction, the rotation speed of the disk is varied so as to make the rate of read data constant and, upon CAV (Constant Angular Velocity) reproduction, the rotation speed of the disk is made constant.
A laser beam is generated and detected at a pickup 12. The laser beam detected at the pickup 12 is converted to an electric signal (pit data) and the pit data is transferred to an RF amplifier 15. The pickup 12 is moved by a servo motor 14 and upon normal reproduction, the pickup 12 is slowly moved in a radial direction as the scanning of the laser beam is made on the track. At a time of a seek operation, the pickup 12 is rapidly moved in the radial direction of the disk 11 across the track.
An RF amplifier 15 generates a servo control signal and RF signal on the basis of the pit data. A servo control circuit 16 generates a servomotor drive signal on the basis of a servo control signal. The servomotor drive signal is supplied through a driver 17 to the servomotor 14. A data slice circuit 18 generates digital data RFDATA on the basis of an RF signal. That is, digital data RFDATA can be obtained by detecting a DSV (Digital Sum Value) containing the RF signal and converting each component in the RF signal to a binary equivalent.
A PLL (Phase Locked Loop).cndot.synchronous signal separating circuit 19 extracts data DATA from the digital data RFDATA, a bit clock PLCK and a synchronous signal PFCK. The data DATA and bit clock PLCK are input to an error correct circuit 20. In the error correct circuit 20, the correction of error data is made using a correct RAM 21.
For the case of a DVD-video for instance, the output data of the error correct circuit 20 is input to an MPEG video decoder 22. The MPEG video decoder 22 outputs a video signal. For the case of a DVD-ROM, the output data of the error correct circuit 20 is input to data buffer 22 and the data buffer 22 outputs the data. The data is transferred to, for example, a computer.
The bit clock PLCK is input to a frequency divider 26. The frequency divider 26 converts the frequency of the bit clock PLCK to a 1/4 (N: an integer). The output signal of the frequency divider 26 is input to the RF amplifier 15. This feedback loop is used to obtain the characteristic (relation between the frequency and a gain) of the RF amplifier corresponding to the data rate of the read data.
A system controller 25 controls a switch circuit 27. For the case of the CLV reproduction, a synchronous signal PFCK representing the data rate is supplied to a disk motor control circuit 24. For the case of a CAV reproduction, a signal FG representing the rotation speed (angular velocity) is applied to the disk motor control circuit 24. The disk motor control circuit 24 generates, based on the clock generated at a crystal oscillator and synchronous signal PFCK or signal FG, a disk motor drive signal which sets a linear velocity (for the case of the CLV reproduction) or angular velocity (for the case of the CAV reproduction) constant. The disk motor drive signal is supplied through a driver 23 to the disk motor 13.
FIG. 2 shows one practical form of the PLL-synchronous signal separating circuit.
Digital data RFDATA output from the data slice circuit is input to a synchronous signal separating circuit 40, phase comparator 41 and relative frequency detector 42. Data DATA is created from the digital data RFDATA. A synchronous signal PFCK is output from the synchronous signal separating circuit 40. An output voltage CONTV of a filter amplifier 43 is determined by an output signal of the phase comparator 41 and output signal of the relative frequency detector 42. A VCO (Voltage Controlled Oscillator) 44 is controlled by the output voltage CONTV.
In this example, the frequency of the output clock of the VCO 44 is converted by frequency dividers 45 to 48 and selector 49 to 1/2.sup.n times (n=0, 1, 2, 3, 4). That is, through the switching of the selector 49 in accordance with the data rate, the frequency division ratio of the output clock of VCO 44 is selected from five combinations (x1, x2, x4, x8, x16). The selector 49 is controlled by a system controller.
The output clock of the selector 49 which has a frequency corresponding to the data rate becomes a bit clock PLCK. Thus the bit clock PLCK is synchronous with the data rate. Further, the bit clock PLCK is input to the synchronous signal separating circuit 40, phase comparator 41 and relative frequency detector 42. Thus the synchronous signal PFCK is also synchronized with the data rate.
The data DATA, bit clock PLCK and synchronous signal PFCK are passed through buffers 52, 53 and 54 and output from the PLL-synchronous signal separating circuit.
The data reproduction method for the disk driver are two kinds: a CLV (Constant Linear Velocity) and CAV (Constant Angular Velocity). In recent years, however, a mainstream has been changed from a system for rotating a disk at a CLV velocity toward a system for rotating a disk at a CAV velocity. The reason is that it is not necessary to change the rotation velocity of the disk for CAV reproduction.
Explanation will be given below about the CLV reproduction and CAV reproduction.
The CLV reproduction is characterized in that, by the rotation velocity of the disk, the velocity (linear velocity) at which the scanning of a laser beam is made on the track of the disk is made constant and hence the rate of the read data is made constant even on any position (radial direction) on the disk. For the CLV reproduction, the data rate is made at all times constant from an innermost circumference to an outermost circumference of the disk and there is an advantage that the processing of the data is easier and less error is produced.
In the CLV reproduction, however, the rotation velocity of the disk varies as set out above. Stated in more detail, the scanning rate of the laser beam at a normal reproduction time is proportional to the irradiation position (radial direction) of the laser and, in order to make the scanning rate of the laser beam constant, the rotation speed of the disk has to be lowered as the irradiation position of the laser beam is moved from the innermost circumference side to the outermost side of the disk. And the maximum value of the rotation speed of the disk becomes about 2.5 times the minimum value.
On the other hand, on the disk drive apparatus used as a computer peripheral equipment, the seek operation (the operation by which the irradiation position of the laser beam is moved across the track) is effected very frequently. For the above-mentioned CLV reproduction, each time the seek operation is effected, the rotation speed of the disk has to be varied greatly.
If the rotation speed of the disk is varied more number of times, there is a disadvantage that a vast power consumption of the disk motor occurs in the driving of the disk. Further, as the power consumption is increased, more heat is generated in the disk motor, thus exerting a bad influence over the driving of the disk drive.
For the CAV reproduction, on the other hand, the advantage of the CLV reproduction acts as a disadvantage and the disadvantage of the CLV reproduction as an advantage. That is, for the CAV reproduction, the rotation speed (angular velocity) of the disk is made at all times constant and the power consumption and heat generation are suppressed to a minimum extent.
For the CAV reproduction, the data rate is varied unlike the CLV reproduction. Stated in more detail, the data rate, that is, the scanning rate (linear rate) of the laser on the disk becomes higher as the irradiation position (radial direction) of the laser beam is moved from the inner circumference side to the outer circumference side. And the maximal value (outermost circumference) of the scanning rate (data rate) of the laser beam becomes about 2.5 times the minimum value (innermost circumference).
In the CD system and DVD system, a plurality of signals having various periods (or frequencies) are contained in the RF signal. For the CD system, for example, a plurality of signals having a period from 3T to 11T are contained where T varies depending upon the data rate. In the DVD system, on the other hand, a plurality of signals are contained having a period from 3T to 14T.
These signals having the different periods have their different amplitudes. For the CD system, it is not performed the equalize-processing because of the CD has a low recording density, therefore, each signal in the RF signal can be accurately converted to a binary equivalent and to achieve a CAV reproduction. For the DVD system, the recording density of the data in the disk is about seven times in comparison with that for the CD system. For the DVD system, therefore, in order to accurately convert the RF signal to a binary equivalent, it is necessary to perform RF equalize processing, that is, make the amplitudes of a plurality of signals by an RF amplifier of a predetermined characteristic (narrow a difference in amplitude of a plurality of signals).
For the DVD system, on the other hand, the data rate of the read data becomes gradually higher, upon CAV reproduction, from the innermost circumference to the outermost circumference of the disk since the rotation speed of the disk is made constant. Further, since that the data rate becomes higher means that an amount of data read in a given period of time is increased, when the data rate becomes higher, the period 3T to 14T of each signal in the RF signal becomes shorter (the frequency becomes higher).
Thus, upon the CAV reproduction, as shown in FIG. 3, the characteristic of the RF amplifier (relation between the frequency and the gain) need to be varied in accordance with a variation of the frequency (period 3T to 14T) in the RF signal. That is, since, upon CAV reproduction, the data rate becomes suddenly higher by the seek action for example, the peak of a gain need be shifted to a higher frequency side (f1.fwdarw.f2.fwdarw.f3) in accordance therewith, while, on the other hand, when the data rate becomes suddenly lower by the seek action, the peak of the gain need be shifted to a lower frequency side (f3.fwdarw.f2.fwdarw.f1) in accordance therewith.
In the DVD system, the equalize processing at the RF amplifier exerts an influence over the probability of generating error data. That is, the accurate performing of the equalize processing at the RF amplifier produces less error and, for this reason, it is very important that the characteristic of the RF amplifier (position of the peak) accurately follow the data rate.
In the conventional disk driver, as shown in FIG. 1, the characteristic of the RF amplifier 15 is varied using the bit clock PLCK which is output from the PLL.cndot.synchronous signal separating circuit 19. The bit clock PLCK is accurately synchronized with the data rate. That is, in the conventional disk driver, the characteristic (position of the peak) of the RF amplifier 15 is so varied as to very rapidly follow a variation of the data rate.
FIG. 4 shows a variation between a control voltage CONTV of the VCO and the frequency of the bit clock PLCK in the case where the irradiation position of the laser beam is continuously (spirally) varied along on the track from the innermost circumference toward the outermost circumference.
The frequency of the bit clock PLCK is proportional to the control voltage CONTV of the VCO. The frequency of the bit clock PLCK becomes fa when the control voltage CONTV of the VCO is Va and becomes fb when the control voltage CONTV of the VCO is Vb, noting that fa/fb is 2.5.
In this case, with an increase of the data rate, the control voltage CONTV of the VCO varies at a rate of a given change from the Vb to the Va. At the same time, the frequency of the bit clock PLCK varies at a rate of a given change from fb to fa (line A). Hence, the peak of the gain at the characteristic of FIG. 3 continuously varies from a lower frequency f.sub.1 to a higher frequency f.sub.3.
In the case where, at the time of a normal reproduction, the irradiation position of the laser beam varies continuously (spirally) from the innermost circumference to the outermost circumference of the disk, the peak of the gain in the characteristic of FIG. 3 also varies to a high frequency in a way to accurately follow an increase of the data rate.
However, a problem arises at a time of a seek motion, for example, in the case where the irradiation position of the laser beam is rapidly varied from the innermost circumference toward the outermost circumference of the disk.
FIG. 5 shows a variation between the control voltage CONTV of the VCO and the frequency of the bit clock PLCK at a time of the seek time, in the case where the irradiation position of the laser beam is rapidly varied from the innermost circumference toward the outermost circumference of the disk.
In this example, the irradiation position of the laser beam is not varied spirally along the track but moved across the track, so that the data rate at the seek time becomes irregularly higher. For this reason, the control voltage CONTV of the VCO is made irregularly higher from Vb to Va and the frequency of the bit clock PLCK goes irregularly higher from fb to fa (line B).
As a result, the peak of the gain for the characteristic of FIG. 3 is irregularly varied, not continuously varied from a lower frequency f1 to a higher frequency f.sub.3. As a result, it becomes impossible to effect the accurate detection of the frequency as well as the comparison of the phases at the PLL.cndot.synchronous separating circuit. In an extreme case, there occurs a vicious cycle such that an abnormal variation in the control voltage CONTV of the VCO causes an abnormal variation in the position of the peak of a gain in the characteristic of FIG. 3 and that an abnormal variation in the position of the peak of the gain in the characteristic of FIG. 3 causes an abnormal variation in the control voltage CONTV of the VCO. If this occurs, the equalize control of the RF amplifier cannot be returned from the abnormal state back to a normal state (line C).
Even at a time of a normal reproduction, if the characteristic of the RF amplifier sensitively responds to the bit clock PLCK, then a jitter in the RF signal is increased and an error is liable to occur.